System and Method for Multiple-Input and Multiple-Output (MIMO) Full-Duplex Precoding Structures

ABSTRACT

Embodiments are provided to enable effective cancellation or reduction of the self-interference (SI) introduced when applying full-duplex (FD) transmission to Multiple-Input-Multiple-Output (MIMO) systems. A method embodiment includes forming, using a precoding matrix generated in accordance with channel conditions, a plurality of beams for a plurality of transmit signals and a plurality of self-interference cancellation signals corresponding to the plurality of transmit signals. The method further includes transmitting, at a plurality of antennas, the plurality of beams for the transmit signals, and receiving, via the plurality of antennas, a plurality of receive signals. A corresponding self-interference cancellation signal is then added to each of the plurality of receive signals to obtain a plurality of corrected receive signals, and the plurality of corrected receive signals are detected at a plurality of receivers.

This application claims the benefit of U.S. Provisional Application No.61/945,507 filed on Feb. 27, 2014 by Tho Le-Ngoc et al. and entitled“Multiple-Input and Multiple-Output (MIMO) Full-Duplex PrecodingStructure,” which is hereby incorporated herein by reference as ifreproduced in its entirety.

TECHNICAL FIELD

The present invention relates to wireless communications and networking,and, in particular embodiments, to a system and method forMultiple-Input and Multiple-Output (MIMO) Full-Duplex precoding.

BACKGROUND

Half Duplex (HD)transmission systems transmit and receive signals inalternate time windows. An HD transceiver will either transmit orreceive a signal in a particular frequency band over single defined timewindow Full-Duplex (FD) transmission systems can both transmit andreceive signals in a given frequency band at the same time. FD systemshave the potential to provide approximately double sum-rate improvementsover HD systems. However, FD systems often suffer from highself-interference. Self-interference refers to the error added to thedetected received signal that can be attributed to reflection and/orleakage of the transmitted signal into the receiver path in the system.Multiple-Input-Multiple-Output (MIMO) transmission systems, wheremultiple antennas are used at both the transmitter and receiver toimprove communication performance, have also been developed. MIMOsystems and techniques can provide increases in data throughput and linkrange without additional bandwidth or increased transmit power incomparison to a single antenna system. These improvements over singleinput single output systems can be achieved by spreading the same totaltransmit power over multiple antennas to achieve at least one of anarray gain that improves the spectral efficiency (more bits per secondper hertz of bandwidth) and/or a diversity gain that improves the linkreliability. There is a need for effective self-interference mitigationto realize the benefits of FD operation in MIMO systems.

SUMMARY OF THE INVENTION

In accordance with an embodiment, a method performed by a networkcomponent for full-duplex communications in a Multiple-Input andMultiple-Output (MIMO) system includes forming, using a precoding matrixgenerated in accordance with channel conditions, a plurality of beamsfor a plurality of transmit signals and a plurality of self-interferencecancellation signals corresponding to the plurality of transmit signals.The method further includes transmitting, at a plurality of antennas,the plurality of beams for the transmit signals, and receiving, via theplurality of antennas, a plurality of receive signals. A correspondingself-interference cancellation signal is then added to each of theplurality of receive signals to obtain a plurality of corrected receivesignals, and the plurality of corrected receive signals are detected ata plurality of receivers.

In accordance with another embodiment, a method performed by a networkcomponent for full-duplex communications in a MIMO system includesforming, using a first precoding matrix generated in accordance withsignal channel conditions, a plurality of beams corresponding to aplurality of transmit signals, and further forming, using a secondprecoding matrix generated in accordance with signal channel conditions,a plurality of self-interference cancellation signals corresponding tothe plurality of transmit signals. The method further includestransmitting, at a plurality of antennas, the plurality of beams for thetransmit signals, and receiving, via the plurality of antennas, aplurality of receive signals. A corresponding self-interferencecancellation signal is then added to each of the plurality of receivesignals to obtain a plurality of corrected receive signals, and theplurality of corrected receive signals are detected at a plurality ofreceivers.

In accordance with yet another embodiment, a network component forfull-duplex communications in a MIMO comprises a processor and anon-transitory computer readable storage medium storing programming forexecution by the processor. The programming includes instructions toform, using a precoding matrix generated in accordance with channelconditions, a plurality of beams for a plurality of transmit signals anda plurality of self-interference cancellation signals corresponding tothe plurality of transmit signals. The network component furthercomprises a plurality of antennas configured to transmit the pluralityof beams for the plurality of transmit signals and to receive aplurality of receive signals, and a plurality of combiners or couplersconfigured to add, to each of the plurality of receive signals, acorresponding self-interference cancellation signal to obtain aplurality of corrected receive signals. The network component alsoincludes a plurality of receivers configured to detect the plurality ofcorrected receive signals.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a full-duplex MIMO point-to-point network;

FIG. 2 illustrates a full-duplex MIMO point-to-multipoint network withhalf-duplex user equipment;

FIG. 3 illustrates a full-duplex MIMO point-to-multipoint network withfull-duplex user equipment;

FIG. 4 illustrates an embodiment of a MIMO full-duplex precodingstructure;

FIG. 5 illustrates an embodiment of a full-duplex operation method thatcan be used for MIMO systems; and

FIG. 6 is a diagram of a processing system that can be used to implementvarious embodiments.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

In MIMO systems, algorithms are used to calculate a precoding channelmatrix that determines the transmission of multiple channels to multipleusers while avoiding (or substantially reducing) signal interferencesbetween the different receiving user equipments (UEs) or mobile stations(MSs). Conventional MIMO systems use HD transmissions. Applying FDtransmission to MIMO systems can provide approximately double sum-rateimprovements over standard HD MIMO systems. However, conventional FDtransmission schemes typically suffer from high self-interference (SI).Embodiments are provided herein to enable effective cancellation (orreduction) of the SI introduced when applying FD transmission to theMIMO system. The embodiments include using a FD precoding structure andan effective full-duplex cancellation scheme that can be implemented inMIMO systems. A MIMO FD Precoding (FDP) structure is used to addressboth beam-forming for the forward or transmit channel andself-interference suppression. The methods discussed herein areapplicable to a plurality of modulation formats including OrthogonalFrequency-Division Multiplexing (OFDM). Those skilled in the art willappreciate that for the sake of ease of presentation, the followingdiscussion will focus on the application of the methods to OFDMtransmissions. The precoding structure allows for various precodingalgorithms and different optimization criteria/objectives to bedeveloped for both point-to-point and point-to-multipoint MIMO FDsystems. Specifically, the structure includes a combination of abeam-former and a self-interference canceller. Such structure providesadditional transmit degrees of freedom.

FIGS. 1, 2, and 3 show embodiments of FD MIMO networks, where theprecoding structure can be used. FIG. 1 illustrates a FD MIMOpoint-to-point network. The FD single-user MIMO network includes anetwork entity 110, e.g., a base station, that serves a user equipment(UE) 120, e.g., a smartphone, a laptop, or any other suitable useroperated device. Both the network entity 110 and the UE 120 cancommunicate using FD transmission (can transmit and receive at the sametime) with multiple antennas according to the MIMO scheme and the FDPstructure described further below. As can be seen from the figures, whentransmitting in FD mode, the transmitted signal can be received by thereceive antenna of the same device. This is a manifestation of theself-interference phenomenon that will be addressed below. FIG. 2illustrates a FD multi-user MIMO network with HD UE. This networkincludes a network entity 210 (e.g., a base station) that servesmultiple UEs 220. In this scenario, the network entity 210 cancommunicate with each UE 220 using FD transmission, while each UE 220communicates with the network entity 210 using HD transmission (e.g.,the UE can either transmit or receive at any particular moment, whilethe network entity can transmit and receive simultaneously). Each one ofthe network entity 210 and UEs 220 use multiple antennas according tothe MIMO scheme. FIG. 3 illustrates a FD MIMO point-to-multipointnetwork with FD UEs. In this scenario, the network entity 310 and theUEs 320 can communicate using FD transmission with multiple antennas.

FIG. 4 illustrates an embodiment of a MIMO FD precoding structure. Theprecoding structure can be part of a FD transmitter/receiver(transceiver) 400 with M transmit/receive antennas, where M is aninteger. For example, the transceiver can correspond to any of thenetwork entities 110, 210 or 310 or to the UEs 120 or 320 with FDcommunications capability in the scenarios above. The M transmit (Tx)signals from transmitter 410 are preprocessed by a precoder 420 using a2M×M precoding matrix. Using the precoding matrix, the precoder 420 actsas a joint beam-former for forward transmission and self-interferencecanceller, for instance with the objective of maximizing the sum-rate.The M Tx signals are split into 2M paths, as shown in FIG. 4. Each ofthe 2M paths includes a Digital-to-Analog Converter (DAC) 430 and anamplifier (Amp) 440.

The 2M paths include a subset of M paths from the precoder 420, referredto herein as M Tx paths, which is used for forward transmission. Each ofthe M Tx paths also include a Power Amplifier (PA) 450, and a circulator470. A circulator is a passive device in which a signal enters one portand is transmitted to the next port by rotation. The circulator 470allows for the transceiver 400 to transmit and receive simultaneouslywhile providing some passive isolation between the M Tx paths from theprecoder 420 and the M receive paths to the M receivers (Rx) 495.However, the transceiver 400 can require significantly more cancellationthan the circulator 470 provides in order to have reliable signaldetection. In another embodiment, an isolator can be used instead of thecirculator 470. The isolator is another passive device that allows forthe transceiver 400 to transmit and receive simultaneously whileproviding isolation between the M Tx paths from the precoder 420 and theM receive paths to the M receivers (Rx) 495.

The 2M paths also include a second subset of M paths to the combiners460, referred to herein as M SI cancellation paths, form an equivalentto an active canceller to cancel the self-interference. However, theobjective of the precoding is not necessarily to focus on minimizing theself-interference. The M SI cancellation paths are connected to theirrespective M receive paths via combiners 460. The combiners are anysuitable devices capable of combining signals together, and are alsoreferred to herein as couplers. Each combiner or coupler 460 ispositioned between a circulator 470 on the corresponding antenna 480side and a low noise amplifier (LNA) 485 and an analog to digitalconverter (ADC) 490 on the corresponding receiver 495 side. In each ofthe M receive paths, the combiner 460 adds an SI signal carried by an SIcancellation path. This effectively mitigates SI in the receivers 495.The SI cancellation signals are calculated using the 2M×M precoder 420with the M Tx paths as part of a joint beam-forming and SI cancellationprecoding. The precoding is established using channel information 430(e.g., H and G channel matrices). The channel information 430 can beobtained via channel measurements, e.g., during a preliminary HDtransmission phase.

The precoding structure of the transceiver 400, as shown in FIG. 4,makes use of MIMO precoding to jointly beam-form the forwardtransmission and cancel the self-interference. As such, the cancellationis done by matrix precoding. Additionally, this structure allows fordifferent optimization objectives (rather than solely minimizingself-interference). For instance, the transmit signals can bepreprocessed using matrix precoding (using the 2M×M precoding matrix atthe precoder 420) to maximize the sum-rate and achieve a trade-offbetween the forward channel beam-forming and the self-interferencesuppression. Hence, the precoding structure provides a more generalizedframework for the optimization of both single-user and multi-userfull-duplex transceivers.

In another embodiment, two separate precoding matrices can be used forthe M Tx paths (forward or transmit channels) and the M SI cancellationpaths (self-interference channels). In this case, one M×M precoder isapplied to the forward channel and another M×M precoder is applied tothe self-interference channels. This approach to separate the 2M×Mprecoding matrix into two M×M precoder matrices corresponds to amatrix-version of an active cancellation approach, where thecancellations are computed via precoding.

Other embodiments include transceivers with dedicated transmit andreceive antennas. Such embodiments would not require the use ofcirculators but would require additional antenna arrangements. Inanother embodiment, the transceivers have different numbers of transmitand receive antennas. In yet another embodiment, the precoding schemeabove is combined with existing passive cancellation techniques. Invarious embodiments, various methods can be used for obtaining channelinformation, including off-line and online measurements and/orestimation techniques.

Other embodiments include joint precoding matrices of differentdimensions than 2M×M. For example, the M transmit signals could beexpanded to 2M transmit signals by padding the original M transmitsignals with M zeros, leading to a 2M×2M square precoding matrix whichmay have some advantages from a mathematical optimization or computationperspective.

One feature of the disclosure is providing a generalized framework foroptimization of both single-user and multi-user FD transceivers. Thedisclosure also allows for different optimization objectives other thanminimizing self-interference (e.g., maximizing sum-rate), and allows forjoint beam-former and self-interference canceller. Another advantage issimplifying implementation for MIMO structures.

In an embodiment, the precoding structure of FIG. 4 above can be appliedat the base station to operate in FD mode and increase the capacity(bits/second/Hertz/area). This is also applicable for small-celldeployments supporting an LTE or next generation networks such as a5^(th) generation (5G) network, for example. The structure can also beapplied at a wireless device (e.g., WiFi) or other non-RAN technologyand benefits both the user and the service provider by providingsignificant capacity increases. FD systems are a strong candidate forincreasing the capacity of wireless networks. The embodiments hereinprovide a practical structure for both point-to-point andpoint-to-multipoint FD systems. Further details of the precodingstructure and the joint use of the beam-former and SI canceller aredescribed by Sean Huberman and Tho Le-Ngoc in a technical paper draftentitled “MIMO Full-Duplex Precoding: A Joint Beamforming andSelf-Interference Cancellation Structure”.

FIG. 5 illustrates an embodiment of a full-duplex operation method thatcan be used for MIMO systems. The method can be implemented using theprecoding structure above. At step 510, M Tx signals corresponding to MMIMO antennas are obtained at a precoder in a transceiver. At step 520,a 2M×M precoding matrix is established at the precoder. Specifically,the 2M×M precoding matrix is established according to channelinformation to form the forward or transmit beams for M Tx signals fromthe precoder to M antennas in accordance with MIMO transmission.Additionally, the 2M×M precoding matrix is established to form M SIcancellation signals from the precoder and achieve self-interferencecancellation in the M receive paths to the M receivers. At step 530, theM SI cancellation signals are added, via combiners (or couplers), to theM receive paths between the receivers and corresponding circulators (orisolators) on the Tx paths. The combination of the M SI cancellationsignals with the respective M received signals to the M receiverseffectively cancels or substantially reduces the SI signal (or SI error)in the M received and hence detected signals by the receivers. At step540, after adding the M SI cancellation signals to the M receive paths,the resulting signals are detected by the M receivers (or detectors).

FIG. 6 is a block diagram of a processing system 600 that can be used toimplement various embodiments. For instance the processing system 600can be part of a UE, such as a smart phone, tablet computer, a laptop,or a desktop computer. The system can also be part of a network entityor component that serves the UE, such as a base station or a WiFi accesspoint. The processing system can also be part of a network component,such as a base station. Specific devices may utilize all of thecomponents shown, or only a subset of the components, and levels ofintegration may vary from device to device. Furthermore, a device maycontain multiple instances of a component, such as multiple processingunits, processors, memories, transmitters, receivers, etc. Theprocessing system 600 may comprise a processing unit 601 equipped withone or more input/output devices, such as a speaker, microphone, mouse,touchscreen, keypad, keyboard, printer, display, and the like. Theprocessing unit 601 may include a central processing unit (CPU) 610, amemory 620, a mass storage device 630, a video adapter 640, and an I/Ointerface 660 connected to a bus. The bus may be one or more of any typeof several bus architectures including a memory bus or memorycontroller, a peripheral bus, a video bus, or the like.

The CPU 610 may comprise any type of electronic data processor. In anembodiment, the processor may serve as a precoder for generating the2M×M precoding matrix, such as the precoder 420. The memory 620 maycomprise any type of system memory such as static random access memory(SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM),read-only memory (ROM), a combination thereof, or the like. In anembodiment, the memory 620 may include ROM for use at boot-up, and DRAMfor program and data storage for use while executing programs. Inembodiments, the memory 620 is non-transitory. The mass storage device630 may comprise any type of storage device configured to store data,programs, and other information and to make the data, programs, andother information accessible via the bus. The mass storage device 630may comprise, for example, one or more of a solid state drive, hard diskdrive, a magnetic disk drive, an optical disk drive, or the like.

The video adapter 640 and the I/O interface 660 provide interfaces tocouple external input and output devices to the processing unit. Asillustrated, examples of input and output devices include a display 690coupled to the video adapter 640 and any combination ofmouse/keyboard/printer 670 coupled to the I/O interface 660. Otherdevices may be coupled to the processing unit 601, and additional orfewer interface cards may be utilized. For example, a serial interfacecard (not shown) may be used to provide a serial interface for aprinter.

The processing unit 601 also includes one or more network interfaces650, which may comprise wired links, such as an Ethernet cable or thelike, and/or wireless links to access nodes or one or more networks 680.The network interface 650 allows the processing unit 601 to communicatewith remote units via the networks 680. For example, the networkinterface 650 may provide wireless communication via one or moretransmitters/transmit antennas and one or more receivers/receiveantennas. In an embodiment, the processing unit 601 is coupled to alocal-area network or a wide-area network for data processing andcommunications with remote devices, such as other processing units, theInternet, remote storage facilities, or the like.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The presented examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method performed by a network component forfull-duplex communications in a Multiple-Input and Multiple-Output(MIMO) system, the method comprising: forming, using a precoding matrixgenerated in accordance with channel conditions, a plurality of beamsfor a plurality of transmit signals and a plurality of self-interferencecancellation signals corresponding to the plurality of transmit signals;transmitting, at a plurality of antennas, the plurality of beams for thetransmit signals; receiving, via the plurality of antennas, a pluralityof receive signals; adding, to each of the plurality of receive signals,a corresponding self-interference cancellation signal to obtain aplurality of corrected receive signals; and detecting, at a plurality ofreceivers, the plurality of corrected receive signals.
 2. The method ofclaim 1, wherein the forming step includes generating the precodingmatrix for the transmit signals to satisfy an objective of maximizing asum-rate of transmission and achieving a trade-off between forwardchannel beam-forming and self-interference suppression.
 3. The method ofclaim 1, wherein the self-interference cancellation signals comprise asame quantity of signals as the beams for the transmit signals, andwherein each one of the self-interference cancellation signalscorresponds to one of the beams for the transmit signals.
 4. The methodof claim 3, wherein the precoding matrix has a size of 2M×M where M isthe quantity of the transmit signals.
 5. The method of claim 3, whereinthe receive signals comprise a same quantity of signals as theself-interference cancellation signals, and wherein each one of theself-interference signals corresponds to one of the receive signals. 6.The method of claim 1, wherein the precoding matrix is formed at aprecoder, and wherein the step of receiving the plurality of receivesignals includes receiving the plurality of receive signals from theplurality of antennas through a plurality of circulators or isolatorspositioned on a plurality of transmit paths between the precoder and theantennas.
 7. The method of claim 6, wherein the self-interferencecancellation signals are added to the receive signals at the pluralityof combiners on a plurality of receive paths between the circulators orisolators and the receivers.
 8. The method of claim 1, whereintransmitting the beams for the transmit signals is done substantiallysimultaneously with receiving the receive signals.
 9. The method ofclaim 1, wherein the network component is one of a wireless basestation, a WiFi access point, and a user equipment.
 10. A methodperformed by a network component for full-duplex communications in aMultiple-Input and Multiple-Output (MIMO) system, the method comprising:forming, using a first precoding matrix generated in accordance withsignal channel conditions, a plurality of beams corresponding to aplurality of transmit signals; forming, using a second precoding matrixgenerated in accordance with signal channel conditions, a plurality ofself-interference cancellation signals corresponding to the plurality oftransmit signals; transmitting, at a plurality of antennas, theplurality of beams for the transmit signals; receiving, via theplurality of antennas, a plurality of receive signals; adding, to eachof the plurality of receive signals, a corresponding self-interferencecancellation signal to obtain a plurality of corrected receive signals;and detecting, at a plurality of receivers, the plurality of correctedreceive signals.
 11. The method of claim 10, wherein theself-interference cancellation signals comprise a same quantity ofsignals as the beams for the transmit signals, and wherein each one ofthe self-interference cancellation signals corresponds to one of thebeams for the transmit signals.
 12. The method of claim 11, wherein eachone of the first precoding matrix and the second precoding matrix has asize of M×M where M is the quantity of the transmit signals.
 13. Anetwork component for full-duplex communications in a Multiple-Input andMultiple-Output (MIMO) system, the network component comprising: aprocessor; a non-transitory computer readable storage medium storingprogramming for execution by the processor, the programming includinginstructions to form, using a precoding matrix generated in accordancewith channel conditions, a plurality of beams for a plurality oftransmit signals and a plurality of self-interference cancellationsignals corresponding to the plurality of transmit signals; a pluralityof antennas configured to transmit the plurality of beams for theplurality of transmit signals and to receive a plurality of receivesignals; a plurality of combiners or couplers configured to add, to eachof the plurality of receive signals, a corresponding self-interferencecancellation signal to obtain a plurality of corrected receive signals;and a plurality of receivers configured to detect the plurality ofcorrected receive signals.
 14. The network component of claim 13 furthercomprising a plurality of circulators or isolators positioned on aplurality of transmit paths between the processor and the plurality ofantennas.
 15. The network component of claim 14, wherein the pluralityof transmit paths include a plurality of digital to analog converters(DACs) and a plurality of amplifiers positioned between the circulatorsor isolators and the processor.
 16. The network component of claim 14,wherein the combiners or couplers are positioned on a plurality ofreceive paths between the circulators or isolators and the plurality ofreceivers.
 17. The network component of claim 16, wherein the pluralityof receive paths include a plurality of low noise amplifiers (LNAs) anda plurality of analog to digital converters (ADCs) positioned betweenthe combiners or couplers and the receivers.
 18. The network componentof claim 16 further comprising a plurality of auxiliary paths betweenthe processor and the plurality of combiners or couplers.
 19. Thenetwork component of claim 18, wherein the plurality of auxiliary pathsinclude a plurality of digital to analog converters (DACs) and aplurality of amplifiers positioned between the processor and thecombiners or couplers.
 20. The network component of claim 19, wherein atotal number of the auxiliary paths is equal to a total number of thetransmit paths and to a total number of the antennas.
 21. The networkcomponent of claim 20, wherein a total number of the receive paths isequal to the total number of the transmit paths and to the total numberof the antennas.